1. Field of the Invention
The present invention relates to an inkjet printer including (i) a recording head operable to eject ink onto a recording medium so as to perform a recording operation on the recording medium, and (ii) an ink source unit provided to store the ink that is to be supplied to the recording head.
2. Discussion of Related Art
There is known an inkjet printer of so-called tube supply type in which the ink is supplied via a flexible tube to the recording head mounted on a movable carriage, from an ink supply source fixed in a stationary body of the inkjet printer, as disclosed in JP-A-S63-17056 and JP-B2-H07-121583.
JP-A-S63-17056 discloses an inkjet printer including a recording head in which a plurality of nozzles are arranged in a vertically extending row. The recording head has recesses formed in its side surface and opening in the side surface, such that the formed recesses define ink delivery passages and a common ink chamber (damper chamber), through which the ink is delivered to the nozzles. The ink passages are all held in communication with the common ink chamber, to which the ink is supplied from an ink tank as the ink source unit fixed to the stationary body of the printer, via the flexible tube. The opening of the recess defining the common ink chamber is sealed with a flexible film (absorber film) which is bonded to the above-described side surface. An oscillator, which is provided by a piezoelectric element, is disposed in a predetermined position in each of the ink passages, so as to be opposed to the above-described side surface. With the oscillator being actuated, the ink in the corresponding ink passages is pressurized, so that the thus pressurized ink is ejected through the corresponding nozzle toward a paper sheet as the recording medium.
JP-B2-H07-121583 discloses an inkjet printer including a recording head in which a plurality of nozzles and ink are arranged in vertically extending rows. On vertically extending, opposite side surfaces of the recording head, there are fixedly disposed piezoelectric elements. Each of the piezoelectric elements is deflected upon application of a drive voltage thereto, whereby the ink is ejected through a corresponding one of the nozzles. On the movable carriage, there is mounted a damper unit (damper-chamber definer), to which the ink is delivered from an ink tank held stationary in a predetermined position, via a flexible tube. The ink delivered to the damper unit is then delivered from the damper unit to ink delivery channels which are defined in the recording head. The damper unit is principally constituted by a first member having an opening in its vertically extending side surface, and a second member having openings in its vertically extending side surfaces. The second member is fixed at one of the vertically extending side surfaces to the first member, with a filter member being gripped by and between the first and second members. The opening in the other vertically extending side surface (which is parallel with the above-described one of the vertically extending side surfaces) of the second member is sealed by a flexible film. The above-described flexible tube is connected at one of its opposite ends to the above-described stationary ink tank, and is connected at the other end to an ink inlet which is formed in a lower portion of the first member, so that the ink tank is held in communication with the ink inlet of the first member. The ink delivery channels of the recording head are held in communication with an ink outlet which is formed in a lower portion of the second member.
In either of the above-described inkjet printers disclosed by JP-A-S63-17056 and JP-B2-H07-121583, the flexible film partially defining the damper chamber serves as a damper wall to damp pressure fluctuation in the ink, which fluctuation is induced as a result of reciprocating motion of the carriage (particularly, upon returning of the carriage), due to an inertia force acting on the ink within the tube connecting the ink tank and the recording head. That is, the flexible film is deformed to absorb the unnecessary change of the ink pressure acting in a direction toward the recording head (nozzles), for enabling the ink to be ejected through the nozzles under substantially a constant pressure.
In either of the above-described inkjet printers in which the damper chamber is of vertical type, one of the vertically extending sides of the damper chamber is defined or sealed by the flexible film, namely, one of vertically extending walls is provided by the flexible film. Where a plurality of recording heads are provided to eject respective different color inks, the damper chambers for the respective different color inks are arranged in a row. In this arrangement, the damper chambers have to be arranged with a predetermined spacing interval between each adjacent pair of those, for allowing the flexible film of each of the damper chambers to be deformed. The arrangement of the damper chambers with the spacing intervals leads to an increase in size of a device to be mounted on the carriage and also an increase in the manufacturing cost due to an increased number of required components. That is, the damper unit equipped with the plurality of damper chambers suffers from these problems.
For solving such problems, the present inventors have designed an arrangement in which one of the damper chambers is adapted to have a relatively small height and a relatively large width while each of the other damper chambers is adapted to have a relatively large height and a relatively small width. The other damper chambers, each having the large height and small width, are arranged in parallel with each other, and are disposed on an upper side of the damper chamber having the small height and large width. In this designed arrangement, a bottom wall of the lower damper chamber having the small height and large width is provided by a flexible film, while upper walls of the above-described other chambers is provided by a flexible film or films. This arrangement enables the damper unit as a whole to be made compact in size and also enables the pressure change in each of the different color inks to be effectively absorbed.
However, in this arrangement, the lower damper chamber disposed under the above-described other chambers has to be to be thin, namely, has to have a sufficiently small height for allowing the other damper chambers to be disposed on the upper side of the lower damper chamber. Due to the small dimension in its height, there is encountered a delay of delivery of the ink in a region which is deviated from a shorted route of the ink flow from an inlet of the lower damper chamber to an outlet of the lower damper chamber. In addition to such a regional poor flow of the ink, the arrangement suffers from a lack of stability in the flow of the ink in the entirety of the lower damper chamber.
Where this arrangement is employed in an inkjet printer arranged to eject four color inks (e.g., black, cyan, yellow and magenta inks), each of three damper chambers as the above-described other chambers disposed on the upper side of another damper chamber as the lower damper chamber has to have a sufficiently small width for allowing the three chambers to be arranged in parallel with each other. Off course, where four or more damper chambers are arranged in parallel with each other, each of the chambers has to have an even smaller width.
Where each of the damper chambers serving as ink delivery chambers or ink storage chambers has such a small width, namely, where each ink passage defined by the chamber has a small width, a liquid is unlikely to rapidly flow along the ink passage, due to a surface tension of the liquid. Such a phenomenon is problematic when a liquid (e.g., an ink, a solution that is temporally stored during transportation of the inkjet printer as a product) is initially introduced into the ink passage, since the introduced liquid is stopped before reaching a downstream end of the ink passage.
Further, in the inkjet printer of tube supply type, since the ink tube has to be displaced in response to movement of the carriage, the ink tube is made of a flexible material. Such a flexible ink tube is likely to allow an atmospheric air to pass therethrough so that the ink within the ink tube is likely to contain the air which takes the form of bubbles. The bubbles, having been once introduced together with the ink into the damper chamber, remain in the damper chamber, even if the damper chamber is subjected to a discharging operation to discharge the bubbles therefrom. That is, in absence of a certain arrangement enabling the bubbles to be immediately discharged from the damper chamber through the outlet, the bubbles remain in the damper chamber, and the bubbles are delivered together with the ink to the ink delivery channels of the recording head, thereby problematically affecting an ink ejection performance of the inkjet printer.
Further, in the inkjet printer of tube supply type, when the carriage is accelerated or decelerated during its reciprocating motion, the acceleration or deceleration is given to the ink within the tube, generating a pressure wave in the ink. The thus generated pressure wave is propagated to the recording head, and the propagated pressure wave affects a meniscus formed at each nozzle of the recording head, thereby resulting in a deterioration in a recording quality.
U.S. Patent Application Publication US 2002/0057320 A1 (corresponding to JP-A-2002-166568) discloses an inkjet printer including a bubble trapper unit (damper unit) which is mounted on the carriage such that the ink is delivered toward the recording head through the bubble trapper unit. The bubble trapper unit has a construction, which separates the bubbles from the ink and accumulates therein, and which absorbs dynamic pressure exerted by the ink. Specifically described, the bubble trapper unit has, in its lower portion, an ink inlet and an ink outlet, such that the ink is delivered from an ink source unit into an inner space of the bubble trapper unit through the ink inlet, and such that the ink is delivered from the inner space of the bubble trapper unit toward the recording head through the ink outlet (see FIG. 3 of US 2002/0057320 A1). The inner space of the bubble trapper unit is sectioned into first and second sections which the above-described ink inlet and outlet face, respectively. The first and second sections are located on respective opposite sides of a metallic net wall which extends upwardly from a bottom wall of the inner space, and are held in communication with each other through a clearance defined by and between an upper wall of the inner space and a top end of the net wall. The first section includes a recessed portion which is formed in the upper wall of the inner space and which is located right above the ink inlet. The recessed portion opens downwardly and serves as a bubble retainer. In a process of manufacturing this trapper unit, the metallic net wall is heat welded to a second member defining the second section, and a first member defining the first section is then ultrasonic welded to a sub-assembly of the second member and the metallic net wall.
In the bubble trapper unit constructed as described above, the dynamic pressure of the ink introduced through the ink inlet is absorbed by the bubbles retained by the bubble retainer provided by the recessed portion. At the same time, the bubbles contained in the ink are floated up toward the upper wall of the inner space, so as to be accumulated in the inner space. When an amount of the accumulated bubbles exceeds a predetermined threshold, a purging operation is carried out. In the purging operation, the bubbles are sucked from a nozzle opening surface of the recording head, so as to be discharged together with the ink out from the bubble trapper unit through the recording head.
In the bubble trapper unit, since the first and second section of the inner space are located on the respective opposite sides of the net wall which serves as a first filter, large bubbles are floated up toward the upper wall of the inner space rather than passing through the net wall. However, small bubbles could be driven by flow of the ink, to pass through the net wall so as to be delivered together with the ink toward the recording head.
As described above, since the bubble trapper unit serves also as a damper unit for absorbing the dynamic pressure of the ink, the inkjet printer as a whole can be made compact in size. However, where the damper unit is used for a considerably frequently used ink such as a black color ink which is supplied to the recording head more in amount than the other color inks, the damper unit is required to have a construction capable of more reliably and effectively absorbing or damping the dynamic pressure of the ink, since the pressure wave propagated through the ink becomes larger as the amount of the supplied ink becomes larger.
Further, since the above-described bubble trapper unit is constituted by the first and second members which are connected with each other with the net wall being interposed therebetween, namely, since the bubble trapper unit is provided by three members to be combined together, a cumbersome operation is required in its manufacturing process. In this sense, there has been a demand for a bubble trapper unit having such a construction that simplifies its manufacturing process.
The above-described bubble trapper unit further has, in addition to the first filter, a second filter which is provided in the ink outlet formed through a lower end of a side wall defining the second section of the inner space (see FIG. 3 of US 2002/0057320 A1). Since the bubble trapper unit is positioned relative to the recording head such that the vertical direction of the second section of the inner space of the bubble trapper unit is held in parallel with the recording head, the ink outlet horizontally extends from a lower end part of the second section toward the recording head. The second filter is disposed in a distal end of the horizontally extending ink outlet, so that an ink passage from the second section toward the second filter includes a bent part. The bent part of the ink passage impedes rapid floatation of the bubbles trapped by the second filter, toward the upper wall of the inner space of the bubble trapper unit. Therefore, the trapped bubbles are likely to remain in vicinity of the second filter and grow to become larger in size. Consequently, the second filter is clogged with the bubbles, thereby impeding flow of the ink through the second filter. If a required amount of the ink is not delivered toward the recording head, the printer would become incapable of satisfactorily ejecting the ink.
Further, while the dynamic pressure of the ink is absorbed by the bubbles retained by the bubble retainer provided in the upper wall of the inner space in the above-described bubble trapper unit, there has been a demand for a still simpler arrangement enabling absorption of the dynamic pressure of the ink with a still higher efficiency.
As described above, if the ink having delivered to the recording head contains bubbles, the bubbles contained in the ink would cause failure in the ink ejection and the consequent deterioration in the quality of the printed image. For avoiding such a deterioration, an bubble trapper such as the above-described bubble trapper unit is provided to separate the bubbles from the ink and accumulate therein. It is therefore necessary to discharge the bubbles accumulated in the bubble trapper.
As a technique of discharging the bubbles from the bubble trapper, JP-A-2000-103084 discloses an inkjet printer including: a recording head mounted on a carriage; a manifold serving as the bubble trapper and disposed on an upper side of the recording head; an ink tank; and a circulation pump. The ink tank and the circulation pump are disposed on a stationary body of the inkjet printer. The circulation pump is operable to circulate the ink between the manifold and the ink tank, so that the bubbles are separated or removed from the ink within the ink tank, which ink has been collected from the manifold. The bubbles remaining in the ink, which has been delivered to the recording head, are sucked from a nozzle opening surface of the recording head, with execution of a purging operation. The bubbles are thus discharged together with the ink from the recording head through the nozzle opening surface.
Further, JP-A-2001-260388 discloses an inkjet printer including: a recording head; a buffer tank disposed on an upper side of the recording head; and an ink tank having a large capacity. In this inkjet printer, the ink is supplied to the buffer tank through a tube, and the bubbles are then separated from the ink in the buffer tank. The ink separated from the bubbles is delivered to the recording head. The bubbles accumulated in the buffer tank is sucked by a pump through a tube which is disposed in an upper portion of the buffer tank. The bubbles are thus discharged from the buffer tank.
Further, in the above-described bubble trapper unit of the inkjet printer disclosed in U.S. Patent Application Publication US 2002/0057320 A1 (corresponding to JP-A-2002-166568), the recessed portion is formed in the upper wall of the inner space of the bubble trapper unit, so that the dynamic pressure of the ink is absorbed by the bubbles retained by the bubble retainer provided by the recessed portion, as described above. The accumulated bubble are discharged from the bubble trapper unit in the purging operation which is effected with the carriage being positioned in a maintenance position. In the purging operation, the bubbles are sucked from the nozzle opening surface of the recording head, so as to be discharged together with the ink from the bubble trapper unit through the recording head. This US Patent Application Publication also teaches that the bubble trapper unit defines a plurality of mutually independent inner spaces (each of which corresponds to the above-described inner space) serving for respective different color inks, wherein the plurality of inner spaces are separated from each other by partition walls and are arranged in parallel with each other.
Where the plurality of mutually independent inner spaces or ink delivery channels are defined in a single body, it is common that the single body is provided by two members. A first member as one of the two members is configured to include a partition wall or walls which separate the ink delivery channels from each other. A second member as the other of the two members is attached to the first member, so as to close openings of the respective ink delivery channels. In this arrangement, if there is a gap between the second member and an end of the partition wall of the first member, there is caused a leakage between two adjacent ink delivery channels which are located on respective opposite sides of the partition wall in question. It is therefore necessary to check if there is a leakage in the unit, by measuring an air pressure within each of the ink delivery channels. The air pressure within each ink delivery channel is measured, while a predetermined amount of pressure is being applied into the ink delivery channel subjected to the measurement, for example, by supplying a pressurized air into the ink delivery channel.
If the above-described single body defines, in addition to the plurality of ink delivery channels, a plurality of bubble discharging channels or ink circulation channels each of which is held in communication with a corresponding one of the ink delivery channels, as disclosed in JP-A-2000-103084 and JP-A-2001-260388, the bubble discharging or ink circulation channels could extend substantially in a direction in which the ink delivery channels are arranged, so that one of the bubble discharging or ink circulation channels could have a part located to be adjacent to at least one of the plurality of ink delivery channels. In this case, it is not possible to simultaneously check a leakage of the at least one of the ink delivery channels and a leakage of one of the ink delivery channels that is held in communication with the above-described one of the bubble discharging or ink circulation channels including the adjacent part. Thus, the number of leakage checking steps required for the plurality of ink delivery channels is inevitably increased.
Meanwhile, there is known an arrangement (see JP-A-2003-237037) in which a driver circuit (operable to activate the recording head) is mounted on the carriage which carries the recording head and which is reciprocatable in a primary scanning direction (i.e., direction perpendicular to a direction in which a recording medium is to be fed). In the inkjet printer having this arrangement, a printing or recording operation is performed by ejecting the ink onto the recording medium through selected ones of the nozzles in response to a drive signal outputted from the driver circuit to the recording head. In the printing operation, each time the signal is outputted from the driver circuit to the recording head, a large amount of electric current momentarily flows through the driver circuit, thereby inducing an abrupt increase in temperature at the driver circuit. Since the number of the nozzles provided in the head unit has been increased for attending a need for printing a higher density of image at a higher speed, the driver circuit has to be equipped with an increased number of driver elements each serving exclusively for a corresponding one of the nozzles. That is, as a result of provision of the increased number of the nozzles, the number of the driver elements provided in the driver circuit has become larger, so that the temperature increase induced at the driver circuit has become more considerable. The considerable temperature increase caused deterioration and instability in electrical properties of the driver circuit, thereby impeding a stable ejection of the ink.
In view of this problem rising from the temperature increase, there has been designed an arrangement, as disclosed in JP-A-2003-237037, in which a heat dissipation unit (heat conductive body) is mounted on the carriage so that heat generated at the diver circuit can be dissipated. In the arrangement disclosed in JP-A-2003-237037, the heat dissipation unit is provided by a plate member which is bent to have a U shape in its cross section, and is fixed relative to the carriage, such that its central bottom portion is held in contact with the driver circuit which is mounted on the carriage, and such that major surfaces of its respective opposite end portions are held in substantially perpendicular to the primary scanning direction (in which the carriage is movable), whereby the generated heat can be effectively dissipated.
In the inkjet printer adapted to perform a full-color printing operation, the recording head is provided with a plurality of ink delivery channels, and the ink delivery unit is provided with a plurality of ink delivery channels which are held communication with the respective ink delivery channels of the recording head. It is preferable that the driver circuit for driving the recording head is positioned relative to the recording head such that a distance therebetween is minimized for minimizing electrical loss caused by an electric resistance. The driver circuit as a heat source is disposed on one of opposite sides of the plurality of ink delivery channels, which sides are opposite to each other in a direction in which the ink delivery channels are arranged. Therefore, the ink delivery channels are distant from the driver circuit by respective different distances, so as to be unevenly affected by the heat generated by the driver circuit. That is, there is inevitably caused difference between the plurality of ink delivery channels in degree of influence exerted thereto by the generated heat. Consequently, the bubbles within the delivery channel close to the driver circuit as the heat source are made to grow faster than those within the other delivery channel or channels.
Where the plurality of ink delivery channels are simultaneously subjected to the bubble discharging operation executed by activation of the circulation pump (as taught by JP-A-2000-103084) or by activation of a suction cap (which is brought into contact with the nozzle opening surface of the recording head), the bubble discharging operation has to be initiated at a point of time at which an amount or volume of bubbles accumulated in the delivery channel close to the driver circuit reaches a predetermined threshold, even if an amount of volume of bubbles accumulated in any other delivery channel has not yet reached the predetermined threshold. This means that the bubble discharging operation has to be executed very frequently. Further, even where the ink delivery channels are individually or independently subjected to the bubble discharging operation, the required number of times of the execution of the discharging operation is inevitably increased with increase of the number of the ink delivery channels. In either of theses cases, therefore, the bubble discharging operation has to be executed such a large number of times, resulting in a poor maneuverability of the inkjet printer. In addition, the large number of times of the execution of the bubble discharging operation leads to an increase in an amount of the ink which is discharged rather than being used for a recording operation.